Secondary battery and method for manufacturing the same

ABSTRACT

The embodiment of the present application relates to the field of Li-ion battery and, in particular, to a secondary battery. The secondary battery includes a cell, a safety component fixed on the cell and thermal conductive adhesive provided between the cell and the safety component, the thermal conductive adhesive contains at least one of hot melt adhesive, silica gel binder or epoxy resin binder, and thermal conductive filling material. The thermal conductive adhesive in the secondary battery performs good thermal conductivity and adhering property, which can stably adhere the safety component with the cell, meanwhile transferring, via the thermal conductive adhesive, heat of the cell to the safety component rapidly, so that the safety component cuts off the circuit to protect the cell during overcharge, thereby avoid situations that the thermal conductive adhesive is separated from the cell due to cell inflation and deformation.

TECHNICAL FIELD

The present application relates to the field of Li-ion battery and, in particular, to a secondary battery containing thermal conductive adhesive and a method for manufacturing the same.

BACKGROUND

Li-ion battery has advantages such as high energy density, long cycle service life, environmental friendly and reproducible etc., which has been widely applied to various kinds of consumer electronic products. However, since the chemical systems of different Li-ion batteries are not the same, safety performance in abuse, in particular overcharge, becomes a great challenge of Li-ion battery. At present, the commonly adopted measure for improving safety performance in abuse is to connect an external protection device, such measure can significantly improve the safety performance of the Li-ion battery in abuse.

Currently, Li-ion battery for commercial use is generally welded with temperature fuse, circuit breaker, PTC and so on outside the battery as the safety protection device, when heat is generated due to abuse of the battery and then the temperature increases, the heat of the battery main body will be conducted to the temperature fuse, when the temperature is higher than the triggering temperature of the temperature fuse, the fuse will open and cut off the circuit, so as to guarantee safety of the battery.

Now in the market, the battery is mainly adhered by double faced adhesive tape, which performs poor thermal conductivity and insufficient adhesion. The present application is aiming at the defects and disadvantages existed in the prior art.

SUMMARY

A primary object of the present application is to provide a secondary battery containing thermal conductive adhesive.

A secondary object of the present application is to provide a method for preparing the secondary battery.

In order to achieve the objects of the present application, the technical solutions adopted are:

The present application relates to a secondary battery, including a cell, a safety component fixed on the cell and thermal conductive adhesive provided between the cell and the safety component, the thermal conductive adhesive contains at least one of hot melt adhesive, silica gel binder or epoxy resin binder, and further contains thermal conductive filling material.

Preferably, the thermal conductive filling material is selected from at least one of metal, metallic oxide, carbon material, nitride, carbide, silicon material.

Preferably, the metal is selected from at least one of silver, copper or tin.

Preferably, the metallic oxide is selected from at least one of aluminium oxide, magnesium oxide, zinc oxide, titanium oxide, SnO_(y), 0<y<=2.

Preferably, the carbon material is selected from at least one of hard carbon, soft carbon, mesocarbon microbead, carbon nano tube, graphite, graphene.

Preferably, the nitride is selected from at least one of silicon nitride, aluminium nitride, boron nitride, titanium nitride.

Preferably, the carbide is selected from at least one of silicon carbide, tungsten carbide.

Preferably, the silicon material is selected from at least one of Si, SiO_(x), 0<x<=2.

Preferably, thermal conductive coefficient of the thermal conductive filling material is 1 W/mK˜10000 W/mK, preferably 20 W/mK˜6000 W/mK.

Preferably, particle size of the thermal conductive filling material is 1 nm˜100 μm, or, the thermal conductive filling material contains thermal conductive filling material particle with particle size larger than 1 nm but smaller than 1 μm, and thermal conductive filling material particle with particle size larger than 1 μm but smaller than 50 μm.

Preferably, the thermal conductive filling material occupies 1%˜99% weight of the thermal conductive adhesive, preferably 20%˜75%.

Preferably, the hot melt adhesive is selected from at least one of polyurethane hot melt adhesive, EVA hot melt adhesive, polyamide hot melt adhesive, polyurethane hot melt adhesive, polyester hot melt adhesive, polyethylene hot melt adhesive, polyesteramide hot melt adhesive, styrene type thermoplastic elastomer; preferably, the polyurethane hot melt adhesive is selected from isocyanate polyurethane prepolymer; preferably, the styrene type thermoplastic elastomer is selected from styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer;

the silica gel binder is selected from silica gel;

the epoxy resin binder contains epoxy resin.

Preferably, the thermal conductive adhesive further contains at least one of tackifier, antioxygen, viscosity modifier.

Preferably, melt viscosity of the thermal conductive adhesive is 1000˜1*10⁶ CPs, initial viscosity is 0.5˜100N, peeling strength is 0.1˜20N/3 mm, melting temperature is 120° C.˜190V, thermal conductive coefficient is 0.1˜10000 W/mK; preferably, the melt viscosity of the thermal conductive adhesive is 1000˜20000 CPs, the initial viscosity is 0.5˜60N, peeling strength is 0.5˜10N/3 mm, melting temperature is 150° C.˜190, thermal conductive coefficient is 0.1˜100 W/mK.

Preferably, area of the thermal conductive adhesive is 1 mm²˜500 mm², thickness of the thermal conductive adhesive is 0.01 mm˜10 mm.

The present application further relates to a method for preparing the secondary battery, including: adding the thermal conductive adhesive on the safety component or the cell, applying a force of 0.1˜100N so that the safety component is tightly adhered with the cell.

The beneficial effect achieved by the present application is:

1. The secondary battery of the present application, through adding thermal conductive filling material in the adhesive so as to prepare thermal conductive adhesive with good thermal conductivity, preferably, the thermal conductive coefficient is within the range of 0.1˜100 W/mK, so that the heat in the cell is transferred to the safety component to keep its temperature the same with that of in the cell and that the circuit is cut off rapidly so as to protect the cell, and improve the safety performance during overcharge.

2. The thermal conductive adhesive of the secondary battery of the present application has good initial viscosity, based on the good viscosity, the safety component is well connected with the cell, thereby avoid situations that the thermal conductive adhesive is separated from the cell due to inflation and deformation of the cell in abuse.

3. The thermal conductive adhesive of the secondary battery of the present application can adopt coating process and is coated on the position of the cell for placing the safety component so as to adhere the safety component with the battery, thereby achieve quantified, positioned adhesive distribution, moreover, the viscosity of the thermal conductive adhesive of the present application increases production efficiency, the consecutive production process is reliable and meets the production process requirements.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a principle diagram of a hot melt adhesive during solidification and adhesion;

FIG. 2 shows variation curves of temperature, voltage and current with respect to time and temperature during overcharging according to Embodiment 1.

FIG. 3 shows variation curves of temperature, voltage and current with respect to time and temperature during overcharging according to Comparison Example 2.

FIG. 4A shows the self-crosslinking reaction of the thermal conductive adhesive.

FIG. 4B shows the reaction between the thermal conductive adhesive and the base material.

The present application will be further illustrated as follows in combination with specific embodiments. It should be understood that, these embodiments are only used to illustrate the present application, rather than limiting the scope of the present application.

DESCRIPTION OF EMBODIMENTS

The present application relates to a secondary battery, including a cell, a safety component fixed on the cell and thermal conductive adhesive provided between the cell and the safety component. The thermal conductive adhesive of the present application is mainly composed of base material and thermal conductive filling material, the base material is selected from at least one of hot melt adhesive, silica gel binder or epoxy resin binder. The safety component includes a circuit breaker, a positive temperature coefficient (Positive Temperature Coefficient, PTC) and a fuse.

As an improvement of the secondary battery of the present application, the thermal conductive filling material is selected from at least one of metal, metallic oxide, carbon material, nitride, carbide, silicon material.

As an improvement of the secondary battery of the present application, the metal is metal powder, which is selected from at least one of silver, copper or tin.

Preferably, the metallic oxide is selected from at least one of aluminium oxide, magnesium oxide, zinc oxide, titanium oxide, SnO_(y), 0<y<=2.

Preferably, the carbon material is selected from at least one of hard carbon, soft carbon, mesocarbon microbead, carbon nano tube, graphite, graphene.

Preferably, the nitride is selected from at least one of silicon nitride, aluminium nitride, boron nitride, titanium nitride.

Preferably, the carbide is selected from at least one of silicon carbide, tungsten carbide.

Preferably, the silicon material is selected from at least one of Si, SiO_(x), 0<x<=2.

The thermal conductive filling material of the present application can also be natural mineral containing the above compounds.

As an improvement of the secondary battery of the present application, the thermal conductive coefficient of the thermal conductive filling material is 1 W/mK˜10000 W/mK (25° C.), preferably 20˜6000 W/mK (25° C.), more preferably 20˜5000 W/mK (25° C.). If the thermal conductive coefficient of the thermal conductive filling material is too small, then the thermal conductive performance of the thermal conductive adhesive will not be affected significantly, however, if too large amount needs to be filled, then the adhering property and mechanical property of the thermal conductive adhesive will be affected.

As an improvement of the secondary battery of the present application, particle size of the thermal conductive filling material is 1 nm˜100 μm, the particle size in the present application refers to the median particle size of the filling material. Too large particle size will lead to insufficient filling degree of the thermal conductive filling material, thus the thermal conductivity is poor; too small particle size will lead to poor processability.

Or, the thermal conductive filling material contains thermal conductive filling material particle with particle size larger than 1 nm but smaller than 1 μm, and thermal conductive filling material particle with particle size larger than 1 μm but smaller than 50 μm, since selecting multiple particle sizes can increase the filling volume and improve thermal conducting effect.

As a thermal conductive filling material with uniform particle size, the particle size is preferably between 20 nm˜10 μm.

As an improvement of the secondary battery of the present application, the thermal conductive filling material occupies 1%˜99% weight of the thermal conductive adhesive, preferably 20%˜75%. Filling too large amount will lead to poor adhering property, filling too small amount will not significantly improve the thermal conducting effect.

If a thermal conductive filling material with thermal conductive coefficient of 25 W/mK˜500 W/mK, the weight occupied by the thermal conductive filling material in the thermal conductive adhesive is preferably 20%˜70%.

If a thermal conductive filling material with thermal conductive coefficient of 1000 W/mK˜5000 W/mK, the weight occupied by the thermal conductive filling material in the thermal conductive adhesive is preferably 1%˜10%.

The hot melt adhesive in the present application is a plastic binder, of which the physical status changes with respect to temperature, but with chemical property unchanged.

As an improvement of the secondary battery of the present application, the hot melt adhesive in the thermal conductive adhesive is selected from at least one of EVA hot melt adhesive, polyamide hot melt adhesive, polyurethane hot melt adhesive, polyester hot melt adhesive, polyethylene hot melt adhesive, polyesteramide hot melt adhesive, styrene type thermoplastic elastomer, the polyurethane hot melt adhesive is selected from isocyanate polyurethane prepolymer, the styrene type thermoplastic elastomer is selected from styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer.

The silica gel binder is selected from silica gel, of which the structural formula is as shown in formula I:

R₁ is selected from substituted or unsubstituted, straight or branched C_(1˜30) alkyl, or substituted or unsubstituted, straight or branched C_(1˜30) alkoxy, R₂ is selected from substituted or unsubstituted, straight or branched C_(1˜30) alkyl, n is an integer in the range of 10˜100.

Preferably, R₁ is selected from substituted or unsubstituted straight or branched C_(1˜20) alkyl or substituted or unsubstituted, straight or branched C_(1˜20) alkoxy, R₂ is selected from substituted or unsubstituted, straight or branched C_(1˜20) alkyl, n is an integer in the range of 10˜100.

For alkyl with 1˜20 carbon atoms, the alkyl can be chainlike alkyl, or can be cyclic alkyl, the hydrogen on the loop of the cyclic alkyl can be replaced by alkyl, lower limit of the number of carbon atoms of the alkyl is preferably 2, 3, 4, 5, the upper limit thereof is preferably 3, 4, 5, 6, 8, 10, 12, 14, 16, 18. Preferably, alkyl with 1˜10 carbon atoms is selected, more preferably, chainlike alkyl with 1˜6 carbon atoms and cyclic alkyl with 3˜8 carbon atoms are selected, furthermore preferably, chainlike alkyl with 1˜4 carbon atoms and cyclic alkyl with 5˜7 carbon atoms are selected. Examples of alkyl can be such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, isoamyl, neo-amyl, hexyl, 2-methyl-amyl, 3-methyl-amyl, 1,1,2-trimethyl-propyl, 3,3,-dimethyl-butyl, heptyl, 2-heptyl, 3-heptyl, 2-methyl hexyl, 3-methyl hexyl, isoheptyl, octyl, nonyl, decyl.

For alkoxy with 1˜20 carbon atoms, lower limit of the number of carbon atoms in the alkoxy is preferably 2, 3, 4, 5, the upper limit thereof is preferably 3, 4, 5, 6, 8, 10, 12, 14, 16, 18. Preferably, alkoxy with 1˜10 carbon atoms is selected, more preferably, alkoxy with 1˜6 carbon atoms is selected, furthermore preferably, alkoxy with 1˜4 carbon atoms is selected. Examples of alkoxy can be such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-amoxy, iso-amoxy, cyclopentoxy, cyclohexoxy.

The epoxy resin binder in the present application contains epoxy resin, which refers to organic compound with two or more epoxy groups contained in a molecule. The molecule structure of the epoxy resin contains active epoxy group, the epoxy group is located at the end or in the middle of the molecule chain or formed as a ring shaped structure. The epoxy resin can perform cross-linking reaction with a plurality types of curing agents to form an insoluble high polymer with a three dimensional net shaped structure.

Structural formula of the epoxy resin adopted by the present application is selected from but not limited to the following structural formulas:

The epoxy resin binder also contains at least one of curing agent, accelerant, flexibilizer, coupling agent, filling material.

The content of the curing agent is 0.01˜90 wt %, the content of the accelerant is 0.01˜90 wt %, the content of the flexibilizer is 0.01˜90 wt %, the content of the coupling agent is 0.01˜90 wt %, the content of the filling material is 0.01˜99 wt %. Specific content can be determined according to the performance requirement on the epoxy resin binder.

The hot melt adhesive is selected from at least one of EVA (ethylene-vinyl acetate copolymer) hot melt adhesive, polyamide hot melt adhesive, polyurethane hot melt adhesive, polyester hot melt adhesive, polyethylene hot melt adhesive, polyesteramide hot melt adhesive, styrene type thermoplastic elastomer.

The ethylene-vinyl acetate copolymer (also called as ethylene-acetic acid ethylene copolymer) is copolymerized by ethylene (E) and vinyl acetate (VA), abbreviated as EVA. In the present application, in order to guarantee adhering property or other properties of the thermal conductive adhesive, ethylene-vinyl acetate copolymer with vinyl acetate (VA) content of 30% is adopted.

The polyamide (PA) in the present application is a general term for a high polymer containing amide group in the repeating unit of its macromolecule main chain. The polyamide can be prepared by open loop polymerizing of acid amide, or can be prepared by polycondensation of diamine and diacid, and so on. PA possesses good overall property, including mechanical property, heat resistant property, wear-resisting property, chemical drug tolerant property and self-lubricating property. There are multiple kinds of PA, including PA6, PA66, PA11, PA12, PA46, PA610, PA612, PA1010 etc. In order to adapt for the adhering property of the thermal conductive adhesive of the present application, PA12 is preferred.

The polyurethane of the present application is a general term of a macromolecular compound containing a repeating carbamate group in its main chain, which is formed by addition polymerization of organic diisocyanate or polyisocyanate with dihydroxyl or polyhydroxy-compound.

The polyethylene (PE) hot melt adhesive in the present application includes HDPE hot melt adhesive and LDPE hot melt adhesive. HDPE powder hot melt adhesive is a non-polar thermoplastic resin with high crystallinity, LDPE powder hot melt adhesive has low melting temperature and good fluidity after melting.

The polyesteramide in the present application is a polymer containing ester bond and amido bond in its molecular chain, which combines the advantages of polyester and polyamide, and includes linear polyesteramide and cross-linking polyesteramide. The present application preferably adopts cross-linking polyesteramide as the hot melt adhesive.

The polyester resin used by the hot melt adhesive of the present application is a thermoplastic product formed by esterification of diacid and dihydric alcohol. Generally, dimethyl terephthalate, isophthalic acid, ethylene glycol and butanediol etc are adopted as raw material of the esterification. Similar to polyamide hot melt adhesive, polyester hot melt adhesive has high heat resistance, good waterproof property and elasticity. The polyester hot melt adhesive is preferably polyether sulfone resin.

In the above hot melt adhesive, the polyurethane hot melt adhesive is preferably isocyanate polyurethane prepolymer, the polymerization reaction formula is:

During the adhering process of the isocyanate polyurethane prepolymer, the solid adhesive is heated to melt as fluid, and then is coated on the surface of the base material, the active end group —NCO group reacts with the active hydrogen in the water absorbed by the surface of the base material, in the air and within the hydroxyl existed on the surface thereof, to form a polyurea structure. The polyurethane binder performs high activity and polarity, and also performs excellent chemical adhesion with base material containing active hydrogen such as porous material like foam, plastic, wood, leather, fabric, paper and ceramic etc, and material having smooth and clean surface such as metal, glass, rubber, plastic etc, which makes the such thermal conductive adhesive fixedly adhere the protection device with the battery.

The principle diagram during solidification and adhesion of the hot melt adhesive is as shown in FIG. 1. The reaction of the isocyanate polyurethane prepolymer during solidification and adhesion is shown in FIGS. 4A-4B. FIG. 4A shows the self-crosslinking reaction of the thermal conductive adhesive. FIG. 4B shows the reaction between the thermal conductive adhesive and the base material.

Compound of isocyanate polyurethane prepolymer with isocyanate group can be selected from: toluene diisocyanate, polymethylene polyphenyl isocyanate, 1,6-hexamethylene diisocyanate, diphenylmethane 4, 4′-diisocyanate, toluene diisocynate etc; compound of the isocyanate polyurethane prepolymer with hydroxyl group can be selected from: polypropylene oxide glycol, poly(ethylene glycol adipate) diol, poly(ethylene-diethylene glycol adipate) diol, poly(ethylene-glycol-propanediol adipate) diol, poly(ethylene glycol adipate) diol.

The styrene series thermoplastic elastomer is selected from styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS).

As an improvement of the secondary battery of the present application, the thermal conductive adhesive can further be added with at least one of tackifier, antioxidant, catalyst, viscosity modifier, so as to adjust the performance of the thermal conductive adhesive.

As an improvement of the secondary battery of the present application, melt viscosity of the thermal conductive adhesive is 1000˜1*10⁶ CPs (175° C.), initial viscosity is 0.5˜100N, peeling strength is 0.1˜20N/3 mm, melting temperature is 120° C.˜190° C., thermal conductive coefficient is 0.1˜100 W/mK (25° C.).

Preferably, the melt viscosity of the thermal conductive adhesive is 1000˜20000 CPs (175° C.), the initial viscosity is 0.5˜60N, peeling strength is 0.5˜10N/3 mm, melting temperature is 150° C.˜190° C., thermal conductive coefficient is 0.1˜50 W/mK (25° C.).

More preferably, the thermal conductive coefficient of the thermal conductive adhesive is 0.2˜50 W/mK (25° C.).

The preparing method of the thermal conductive adhesive of the present application is: in water-free inert gas environment, adding thermal conductive filling material after heating the raw material, stirring the mixture to be dispersed and uniform, then sealing.

As an improvement of the secondary battery of the present application, the area of the thermal conductive adhesive is 1 mm²˜500 mm², the thickness of the thermal conductive adhesive is 0.05˜5 mm.

The preparing method of the secondary battery according to the present application is: adding thermal conductive adhesive on the safety component or the cell, applying a force of 0.1˜100N so that the safety component tightly adheres to the cell. Preferably, the operating temperature of the thermal conductive adhesive is 150˜200° C.

The adding manner of the thermal conductive adhesive in the present application can be coating, depositing, adhering, placing etc; the coating manner can be achieved by dotting, coating line, spraying etc.

The isocyanate polyurethane prepolymer, silica gel, epoxy resin used in the embodiments of the present application are purchased from Guangzhou Yawei company.

The ethylene-vinyl acetate copolymer (EVA), polyamide (PA), low density polyethylene (LDPE), polyesteramide (PEA) used in the embodiments of the present application are purchased from Huagongbaichuan company.

The double faced adhesive tape 3M467, thermal conductive double faced adhesive tape 3M8805 used in the embodiments of the present application are purchased from 3M company.

The high density polyethylene (HDPE), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS) used in the embodiments of the present application are purchased from Shenzhen Suyuanshiye Co, Ltd.

Embodiments 1˜9

Preparing thermal conductive adhesive according to the hot melt adhesive and electrical conductive filling material shown in Table 1, and coating the prepared thermal conductive adhesive between the cell and the safety component, detecting the performance of the cell.

The preparing method of the thermal conductive adhesive: in water-free inert gas environment, adding thermal conductive filling material after heating the raw material, stirring the mixture to be dispersed and uniform, then sealing.

The preparing method of the battery is: adding thermal conductive adhesive on the safety component or the cell, applying a force of 0.1˜100N so that the safety component is tightly adhered with the cell. Preferably, the operating temperature of the thermal conductive adhesive is 150˜200° C.

TABLE 1 Thermal conductive filling material Thermal Weight Particle conductive ratio size coefficient No. Hot melt adhesive Type (%) (nm) (W/mK) Embodiment 1 polypropylene oxide aluminium 50% 500 30 glycol, toluene diisocynate oxide Embodiment 2 polymethylene polyphenyl graphite 50% 500 151 isocyanate, poly(ethylene glycol adipate) diol Embodiment 3 1,6-hexamethylene diisocyanate, SiC 50% 500 83 poly(ethylene-diethylene glycol adipate) diol Embodiment 4 diphenylmethane 4,4′- Silver 20% 500 420 diisocyanate, poly(ethylene- powder glycol-propanediol adipate) diol Embodiment 5 toluene diisocyanate, aluminium 65% 400 30 poly(ethylene glycol adipate) diol oxide Embodiment 6 EVA (VA 30 wt %) aluminium 50% 500 30 oxide Embodiment 7 PA12 aluminium 50% 500 30 oxide Embodiment 8 LDPE aluminium 50% 500 30 oxide Embodiment 9 PEA aluminium 50% 500 30 oxide Comparison Double faced adhesive — — — — example 1 tape 3M467 Comparison — — — — — example 2 Comparison Thermal conductive double — — — — example 3 faced adhesive tape 3M8805

The performance of the thermal conductive adhesive in Embodiments 1˜9 and Comparison examples 1˜3 is as shown in Table 2:

TABLE 2 Thermal conductive Oper- coefficient ating of thermal Melt temper- Initial Peeling conductive viscos- ature/ viscos- Setting strength adhesive/ No. ity/CPs ° C. ity/N time/h N/3 mm W/mK Embodi- 6000 170 50 18 8 1.1 ment 1 Embodi- 5000 180 60 20 7 1.5 ment 2 Embodi- 5500 180 50 24 8.4 1.4 ment 3 Embodi- 5000 175 45 20 7.9 2.5 ment 4 Embodi- 6500 180 45 20 7.5 1.6 ment 5 Embodi- 4800 180 60 10 10 1.1 ment 6 Embodi- 5000 190 55 12 9 1.4 ment 7 Embodi- 4400 185 45 10 7 1.2 ment 8 Embodi- 4500 175 40  8 6 1.1 ment 9 Comparison — — 8 — 2  0.12 example 1 Comparison — — — — — — example 2 Comparison — — 5 — 2 0.7 example 3

The detection method includes:

(i) initial viscosity testing method: preparing sample product with 0.03 mg/mm dispensing adhesive, cutting a sample product of 3 mm*20 mm, cementing TCO after dispensing adhesive, and testing tension under normal temperature within 2 minutes after completion of the sample product.

(ii) peeling strength testing method: preparing adhering sample product with 0.06 mg/mm dispensing adhesive, cutting a sample product with 3 mm width, cementing TCO after dispensing adhesive, then testing to acquire performance of the battery by peeling at 180° C.

(iii) overcharge testing method: charging using a constant current of 1 C to a voltage of 10V, then stopping testing after maintaining CV as 10V for 2 h or until the temperature of the cell is below 40° C. Variation curves of temperature, voltage and current at different time and under different temperature of Embodiment 1 and Comparison example 2 are shown in FIG. 2 and FIG. 3, respectively.

The performance of the battery acquired by testing is as shown in Table 3:

TABLE 3 Highest Safety Testing temperature Highest component result of on surface temperature cut off battery of safety on surface No. or not overcharge component/° C. of cell/° C. Embodi- Yes Nonignition 80 80 ment 1 Embodi- Yes Nonignition 82 85 ment 2 Embodi- Yes Nonignition 75 76 ment 3 Embodi- Yes Nonignition 86 87 ment 4 Embodi- Yes Nonignition 74 76 ment 5 Embodi- Yes Nonignition 79 80 ment 6 Embodi- Yes Nonignition 78 78 ment 7 Embodi- Yes Nonignition 87 88 ment 8 Embodi- Yes Nonignition 89 90 ment 9 Compar- No Ignition 600 580 ison ex- ample 1 Compar- None Ignition — 850 ison ex- ample 2 Compar- Yes Nonignition 80 94 ison ex- ample 3

Embodiment 2

Preparing thermal conductive adhesive according to the hot melt adhesive and thermal conductive filling material shown in Table 4, and coating the prepared thermal conductive adhesive between the cell and the safety component, detecting the performance of the cell. The preparing method is as the same with Embodiment 1.

TABLE 4 Thermal conductive filling material Thermal weight conductive ratio Particle coefficient No. Hot melt adhesive Type (%) size (W/mK) Embodiment 10 HDPE graphene  1% 10 nm 4800 Embodiment 11 SBS mesocarbon 50% 100 nm 200 microbead Embodiment 12 SIS carbon  5% 50 nm 1500 nano tube Embodiment 13 EVA (VA 30 wt %) SnO₂ 20% 6 μm 30 Embodiment 14 EVA (VA 30 wt %) Si 65% 400 nm 100 Embodiment 15 Silica gel silicon 50% 4 μm 200 nitride Embodiment 16 Silica gel aluminium 50% 5 μm 30 oxide Embodiment 17 Epoxy resin: formula 1 magnesium 50% 5 μm 36 oxide Embodiment 18 Epoxy resin: formula 2 hard carbon 20% 5 μm 50 Embodiment 19 Epoxy resin: formula 3 soft carbon 65% 5 μm 20 Embodiment 20 Epoxy resin: formula 1 silicon 50% 5 μm 83 carbide Embodiment 21 polypropylene oxide glycol, zinc oxide 20% 3 μm 26 toluene diisocynate Embodiment 22 polymethylene polyphenyl aluminium 30% 6 μm 30 isocyanate, poly(ethylene nitride glycol adipate) diol Embodiment 23 1,6-hexamethylene boron 40% 3 μm 125 diisocyanate, nitride poly(ethylene-diethylene glycol adipate) diol Embodiment 24 diphenylmethane titanium 50% 4 μm 29 4,4′-diisocyanate, nitride poly(ethylene glycol adipate) diol Embodiment 25 EVA (VA 30 wt %) SiO₂ 60% 15 μm 5 Embodiment 26 polypropylene oxide glycol, aluminium 50% 6 μm 25% 30 toluene diisocynate oxide 800 nm 25% Embodiment 27 polyester hot melt adhesive zinc oxide 50% 3 μm 25% 26 500 nm 25% Embodiment 28 1,6-hexamethylene Si 50% 20 μm 100 diisocyanate, poly(ethylene-diethylene glycol adipate) diol Embodiment 29 diphenylmethane Si 50% 50 μm 100 4,4′-diisocyanate, poly(ethylene-glycol- propanediol adipate) diol Embodiment 30 toluene diisocynate, Si 50% 100 μm 100 poly(ethylene glycol adipate) diol

The performance of the thermal conductive adhesive in Embodiments 10˜30 is as shown in Table 5:

TABLE 5 Thermal conductive Oper- coefficient ating of thermal Melt temper- Initial Peeling conductive viscos- ature/ viscos- Setting strength adhesive/ No. ity/CPs ° C. ity/N time/h N/3 mm W/mK Embodi- 6500 170 45 12 6 3.5 ment 10 Embodi- 5500 180 50 13 6.5 2.4 ment 11 Embodi- 5500 180 42 15 7 1.5 ment 12 Embodi- 4800 185 45 13 8 0.9 ment 13 Embodi- 7000 170 35 12 5.5 1.9 ment 14 Embodi- 6000 180 40 18 7 2.5 ment 15 Embodi- 6200 180 42 18 8 1.8 ment 16 Embodi- 1000 25 0.5 72 7 0.9 ment 17 Embodi- 800 25 0.6 72 6.8 0.6 ment 18 Embodi- 1200 25 0.5 72 7 0.9 ment 19 Embodi- 1300 25 0.4 72 6 1.5 ment 20 Embodi- 4500 175 45 14 6.5 0.5 ment 21 Embodi- 4700 175 40 16 6 0.8 ment 22 Embodi- 5000 175 40 16 5.8 1.6 ment 23 Embodi- 5500 175 35 18 5 0.9 ment 24 Embodi- 5500 180 30 16 5 0.25 ment 25 Embodi- 5500 180 30 16 8 2.1 ment 26 Embodi- 6000 180 28 12 4 0.4 ment 27 Embodi- 6500 180 16 18 4 1.2 ment 28 Embodi- 5800 180 14 16 3.5 0.9 ment 29 Embodi- 5000 180 9 12 1 0.6 ment 30

The performance of the battery acquired by testing is as shown in Table 6:

TABLE 6 Highest Safety Testing temperature Highest component result of on surface temperature cut off battery of safety on surface No. or not overcharge component/° C. of cell/° C. Embodi- Yes Nonignition 75 75 ment 10 Embodi- Yes Nonignition 76 77 ment 11 Embodi- Yes Nonignition 77 81 ment 12 Embodi- Yes Nonignition 76 89 ment 13 Embodi- Yes Nonignition 77 79 ment 14 Embodi- Yes Nonignition 75 79 ment 15 Embodi- Yes Nonignition 78 80 ment 16 Embodi- Yes Nonignition 78 92 ment 17 Embodi- Yes Nonignition 76 98 ment 18 Embodi- Yes Nonignition 77 94 ment 19 Embodi- Yes Nonignition 76 79 ment 20 Embodi- Yes Nonignition 77 85 ment 21 Embodi- Yes Nonignition 76 82 ment 22 Embodi- Yes Nonignition 75 77 ment 23 Embodi- Yes Nonignition 76 83 ment 24 Embodi- Yes Nonignition 76 92 ment 25 Embodi- Yes Nonignition 74 75 ment 26 Embodi- Yes Nonignition 78 86 ment 27 Embodi- Yes Nonignition 78 92 ment 28 Embodi- Yes Nonignition 79 95 ment 29 Embodi- Yes Nonignition 82 104 ment 30

Comparison Examples 4˜9

Preparing thermal conductive adhesive according to the hot melt adhesive and electrical conductive filling material shown in Table 7, and coating the prepared thermal conductive adhesive between the cell and the safety component, detecting the performance of the cell. The preparing method is as the same with Embodiment 1.

TABLE 7 Thermal conductive filling material Thermal Weight conductive ratio Particle coefficient Hot melt adhesive Type (%) size (W/mK) Comparison polypropylene oxide glycol aluminium 50% 110 μm  30 example 4 and toluene diisocynate oxide Comparison polypropylene oxide glycol ABS 50% 5 μm 0.25 example 5 and toluene diisocynate Comparison polypropylene oxide glycol — — — — example 6 and toluene diisocynate Comparison polypropylene oxide glycol aluminium  1% 5 μm 30 example 7 and toluene diisocynate oxide Comparison polypropylene oxide glycol aluminium 80% 5 μm 30 example 8 and toluene diisocynate oxide Comparison polypropylene oxide glycol aluminium 95% 5 μm 30 example 9 and toluene diisocynate oxide

The performance of the thermal conductive adhesive and the battery prepared by the thermal conductive adhesive of Comparison examples 4˜9 is as shown in Table 8 and

Table 9:

TABLE 8 Thermal Oper- conduc- ating tive Melt temper- Initial Peeling coeffi- viscos- ature/ viscos- Setting strength cient/ ity/CPs ° C. ity/N time/h N/3 mm W/mK Comparison 7000 180 10 16 3 1.1 example 4 Comparison 5500 175 30 12 6 0.3 example 5 Comparison 4000 175 50 14 12 0.08 example 6 Comparison 4300 180 50 16 10 0.4 example 7 Comparison 4400 180 48 15 9.8 0.5 example 8 Comparison 8000 180 10 8 2 2.8 example 9

TABLE 9 Highest Safety Testing temperature Highest component result of on surface temperature cut off battery of safety on surface or not overcharge component/° C. of cell/° C. Comparison Yes Nonignition 79 102 example 4 Comparison No Ignition 520 580 example 5 Comparison No Ignition 630 700 example 6 Comparison Yes Nonignition 79 86 example 7 Comparison Yes Nonignition 75 76 example 8 Comparison No (fall Ignition 600 750 example 9 off)

The experiment result of Comparison example 4 shows that if the particle size of the thermal conductive filling material is too large, the thermal conductive coefficient decreases.

The experiment results of Comparison examples 5 and 6 show that if the thermal conductive filling material is not added, or filling material with relative low thermal conductive coefficient is added, the thermal conductivity of the prepared thermal conductive adhesive cannot be effectively improved;

The experiment results of Comparison examples 7˜9 show that with thermal conductive filling material of moderate thermal conductivity added, if too much is added, the physical property of the thermal conductive adhesive will be affected due to poor adhesion, thereby cannot form a stable connection with the battery and the safety component.

Although the present application is illustrated by the preferred embodiments as above, however, they are not used to limit the claims; various modifications and variations can be made by those skilled in the art without departing from the concept of the present application, therefore, the protection scope of the present application shall be defined by the scope of the claims. 

What is claimed is:
 1. A secondary battery, comprising a cell, a safety component fixed on the cell and thermal conductive adhesive provided between the cell and the safety component, wherein, the thermal conductive adhesive comprises: an isocyanate polyurethane prepolymer and aluminum oxide, wherein, the thermal conductive adhesive further comprises at least one of a tackifier or an antioxygen.
 2. The secondary battery according to claim 1, wherein, a particle diameter of the aluminum oxide is 1 nm to 100 μm.
 3. The secondary battery according to claim 1, wherein the thermal conductive adhesive comprises 1% to 99% aluminum oxide by weight.
 4. The secondary battery according to claim 1, wherein, the thermal conductive adhesive has a melt viscosity of 1·10³ to 1·10⁶ CPs, an initial viscosity of 0.5 to 100N, a peeling strength of 0.1 to 20N/3 mm, a melting temperature of 120 to 190° C., and a thermal conductive coefficient of 0.1 to 100 W/mK.
 5. The secondary battery according to claim 1, wherein an area of the thermal conductive adhesive is 1 mm² to 500 mm², and a thickness of the thermal conductive adhesive is 0.01 mm to 10 mm.
 6. A method for preparing the secondary battery according to claim 1, comprising the steps of: adding the thermal conductive adhesive on the safety component or the cell, wherein the thermal conductive adhesive comprises the isocyanate polyurethane prepolymer and the aluminum oxide, and, applying a force of 0.1 to 100N to the safety component, so that the safety component is adhered to the cell.
 7. The secondary battery according to claim 1, wherein the thermal conductive adhesive comprises 20% to 75% aluminum oxide by weight.
 8. The secondary battery according to claim 1, wherein the thermal conductive adhesive has a melt viscosity of 1000 to 20000 CPs, an initial viscosity of 0.5 to 60N, a peeling strength of 0.5 to 10N/3 mm, a melting temperature of 150° C. to 190° C., and a thermal conductive coefficient of 0.1 to 100 W/mK. 